Characteristics, formation, and sources of PM in 2020 in Suzhou, Yangtze River Delta, China.

Here we present seasonal chemical characteristics, formations, sources of PM in the year 2020 in Suzhou, Yangtze River Delta, China. Expectedly, organic matter (OM) found to be the most dominant component of PM, with a year-average value of 10.3 ± 5.5 μg m, followed by NO (6.7 ± 6.5 μg m), SO (3.3 ± 2.5 μg m), NH (3.2 ± 2.8 μg m), EC (1.1 ± 1.3 μg m), Cl (0.57 ± 0.56 μg m), Ca (0.55 ± 0.91 μg m), K (0.2 ± 1.0 μg m), Na (0.18 ± 0.45 μg m), and Mg (0.09 ± 0.15 μg m). Seasonal variations of PM showed the highest average value in spring, followed by winter, fall, and summer. Meanwhile, the formation mechanisms of the major PM species (NO, SO, and OM) varied in seasons. Interestingly, NO may have the highest conversion rate to NO in spring, which might be linked with the nighttime chemistry due to the high relative humidity. Moreover, OM in summer was mainly produced by the daytime oxidation of volatile organic compounds, while local primary organic aerosols might play a significant role in other seasons. Source apportionment showed that the more-aged PM contributed significantly to the PM mass (42%), followed by the dust-related PM (38%) and the less-aged PM (21%). Potential contribution source function (PSCF) results indicated that aged PM were less affected by transportation than dust-related PM.